Interleukin-22 (IL-22) is a member of the IL-10 family of cytokine that is produced by Th22 cells. NK cells, lymphoid tissue inducer (LTi) cells, dendritic cells and Th17 cells. IL-22 binds to the IL-22R1/IL-10R2 receptor complex, which is expressed in innate cells such as epithelial cells, hepatocytes, and keratinocytes and in barrier epithelial tissues of several organs including dermis, pancreas, intestine and the respiratory system.
IL-22 plays an important role in mucosal immunity, mediating early host defense against attaching and effacing bacterial pathogens. See Zheng et al., 2008, Nat. Med. 14:282-89. IL-22 promotes the production of anti-microbial peptides and proinflammatory cytokines from epithelial cells and stimulates proliferation and migration of colonic epithelial cells in the gut. See Kumar et al., 2013, J. Cancer, 4:57-65. Upon bacterial infection, IL-22 knock-out mice displayed impaired gut epithelial regeneration, high bacterial load and increased mortality. Kumar et al., supra. Similarly, infection of IL-22 knock-out mice with influenza virus resulted in severe weight loss and impaired regeneration of tracheal and bronchial epithelial cells. Thus, IL-22 plays a pro-inflammatory role in suppressing microbial infection as well as an anti-inflammatory protective role in epithelial regeneration in inflammatory responses. Much of IL-22's biological action promoting pathological inflammation and tissue repair remains to be determined. The seemingly conflicting reports on the effects of IL-22 on epithelial cells are not yet thoroughly understood. Kumar et al., supra.
The regulation of antimicrobial defensins, which limits bacterial replication and dissemination, would help to stabilize intestinal microbiota by reducing subsequent LPS production, and preserving mucosal integrity. IL-22 up-regulates expression of acute phase proteins, including SAA, and contributes to the expression of a range of genes associated with acute inflammatory responses, including IL-6, G-CSF, and IL-1a. Systemic administration of IL-22 to healthy mice also up regulates LPS binding proteins to physiologically relevant concentrations for neutralizing LPS in response to bacterial infection.
Increased expression of IL-22 is detected in inflammatory bowel disorder (IBD) patients. See e.g., Wolk et al., 2007, J. Immunology, 178:5973; Andoh et al., 2005, Gastroenterology, 129:969. IBDs such as Crohn's disease (CD) and ulcerative colitis (UC) are thought to result from a dysregulated immune response to the commensal microflora present in the gut. Cox et al., 2012, Mucosal Immunol. 5:99-109. Both UC and CD are complex diseases that occur in genetically susceptible individuals who are exposed to as yet poorly-defined environmental stimuli. CD and UC are mediated by both common and distinct mechanisms and exhibit distinct clinical features. See Sugimoto et al. 2008, J. Clinical Investigation, 118:534-544.
In UC, inflammation occurs primarily in the mucosa of the colon and the rectum, leading to debilitating conditions including diarrhea, rectal bleeding, and weight loss. It is thought that UC is largely caused by an inappropriate inflammatory response by the host to intestinal microbes penetrating through a damaged epithelial barrier (Xavier and Podolsky, 2007, Nature 448:427-434). Crohn's disease is characterized by intestinal infiltration of activated immune cells and distortion of the intestinal architecture. See Wolk et al., supra.
In recent years, a number of drugs based on various strategies to regulate the immune response have been tested to treat IBD, including steroids, immunomodulators, and antibodies against inflammatory cytokines, with variable success (Pastorelli et al., Expert opinion on emerging drugs, 2009, 14:505-521). The complex variety of gut flora contributes to the heterogeneity of the disease. Thus, there is a need for a better therapeutics for IBD.
Cardiovascular disease (CVD) is a leading cause of mortality that results, in part, from atherosclerotic disease of large blood vessels. Atherosclerosis is the major culprit in CVD events and is a slow and progressive disease that results from hypercholesterolemia and chronically inflamed blood vessels. Atherosclerotic lesions are characterized as lipid laden with infiltration of immunocytes, especially macrophages and T cells. It is now acknowledged that both the innate and adaptive immune mechanisms contribute to the progression and eventual thrombosis of the atherogenic plaque (Ross, Am Heart J. 1999 November; 138 (5 Pt 2):S419-20; Hansson 2005 N Engl J Med 352(16): 1685-95; Hansson and Hermansson 2011 Nature Immunology 12(3): 204-12).
Acute pancreatitis (AP) is an acute inflammatory process of the pancreas. Acute kidney injury (AKI) is an abrupt loss of kidney function, resulting in the retention of urea and other nitrogenous waste products and in the dysregulation of extracellular volume and electrolytes. AKI was previously known as acute kidney failure. The change reflects recent recognition that even smaller decreases in kidney function that do not result in overt organ failure are of substantial clinical relevance and are associated with increased morbidity and mortality. There remains a need for better treatment for AP and AKI.
Metabolic syndrome is a complex state characterized by a series of risk factors that contribute to thrombosis, hypertension, dyslipidemia, and inflammation. Insulin resistance and obesity are major pathogenic mechanisms underlying the metabolic syndrome.
Insulin resistance increases CVD risk because it induces endothelial dysfunction which, in combination with atherogenic dyslipidemia, inflammation, and hypertension, contributes to the mortality from coronary artery disease (CAD). Persistent insulin resistance also increases the chance of developing diabetes mellitus type 2 (T2DM) although the atherogenic state occurs many years before the onset of T2DM. It is likely therefore that the natural history of CAD lies in the same pathway as T2DM but begins much earlier in life in a subclinical form, taking longer to manifest clinically, with or without the presence of diabetes.
The term metabolic endotoxemia was coined to describe the condition of increased plasma LPS induced by, for example, high-fat high-calorie diet (HFD) (Cani et al. 2007. Diabetes 56(7): 1761-72). Mice fed with HFD have increased plasma levels of bacterial lipopolysaccharide (LPS) and this elevation appears to be a direct consequence of the increased dietary fat (Cani et al. 2007 supra; Cani et al. 2008 Diabetes 57(6): 1470-81; Ghoshal et al. 2009, J Lipid Res 50(1): 90-7). There is compelling evidence that gut microbiota play an integral part in the host's energy balance and harvest of dietary nutrients and carbohydrate metabolism, through modulation of gut mucosal epithelial cell function (Turnbaugh et al. 2009, J Physiol (Lond) 587(Pt 17): 4153-8; Manco et al. 2010, Endocr Rev 31(6): 817-44). Alteration in gut microbiota that occurs through disproportionate dietary fat composition or excess dietary caloric consumption is a recognized initiator of obesity and insulin resistance, the established sequela of cardiovascular disease. Lipopolysaccharides are found in outer membrane of gram-negative bacteria and act as a source of endotoxin that can elicit a strong immune response (Barcia et al. Clin Infect Dis 41 Suppl 7: S498-503). Alterations in the population, species and regional distribution of intestinal microbiota can lead to changes in catabolism of LPS and a high fat diet will facilities adsorption of LPS across the intestinal barrier. Under these conditions, increased LPS in systemic circulation will induce low grade chronic inflammation, activating the endogenous protective host response to elevate plasma lipids that, in the chronic condition, contributes to diet induced obesity, insulin resistance and atherosclerosis, and eventual CVD events.
Diabetes mellitus is a serious metabolic disease that is defined by the presence of chronically elevated levels of blood glucose (hyperglycemia). This state of hyperglycemia is the result of a relative or absolute lack of activity of the peptide hormone, insulin. Insulin is produced and secreted by the β cells of the pancreas. Insulin is reported to promote glucose utilization, protein synthesis, and the formation and storage of carbohydrate energy as glycogen. Glucose is stored in the body as glycogen, a form of polymerized glucose, which can be converted back into glucose to meet metabolism requirements. Under normal conditions, insulin is secreted at both a basal rate and at enhanced rates following glucose stimulation, all to maintain metabolic homeostasis by the conversion of glucose into glycogen. There remains a need for new treatment paradigms for atherosclerosis and prevention of CVD events, metabolic syndrome, acute endotoxemia and sepsis, and insulin-related disorders.
Wound healing is a complex process, involving an inflammation phase, a granulation tissue formation phase, and a tissue remodeling phase (see, e.g., Singer and Clark, Cutaneous Wound Healing, N. Engl. J. Med. 341:738-46 (1999)). These events are triggered by cytokines and growth factors that are released at the site of injury. Many factors can complicate or interfere with normal adequate wound healing. For example, such factors include age, infection, poor nutrition, immunosuppression, medications, radiation, diabetes, peripheral vascular disease, systemic illness, smoking, and stress.
For subjects with diabetes, a chronic, debilitating disease, development of a diabetic foot ulcer (also referred to as a wound) is a common complication. A chronic ulcer is defined as a wound that does not proceed through an orderly and timely repair process to produce anatomic and functional integrity (see, e.g., Lazarus et al., Definitions and guidelines for assessment of wounds and evaluation of healing, Arch. Dermatol. 130:489-93 (1994)). By its nature, the diabetic foot ulcer is a chronic wound (American Diabetes Association, Consensus development conference on diabetic foot wound care, Diabetes Care, 22(8):1354-60 (1999)). Because the skin serves as the primary barrier again the environment, an open refractory wound can be catastrophic; a major disability (including limb loss) and even death can result. Foot ulceration is the precursor to about 85% of lower extremity amputations in persons with diabetes (see, e.g., Apelqvist, et al., What is the most effective way to reduce incidence of amputation in the diabetic foot? Diabetes Metab Res. Rev., 16(1 Suppl.): S75-S83 (2000)). Thus, there is a need for accelerating or improving wound healing, including diabetic wound healing.